In order to determine the organ preference and relative distances between apposed infected red cells and vessel endothelia, distribution patterns of three strains of Plasmodium falciparum will be studied in two species of New World monkeys (Aotus trivirgatus and Saimiri sciureus) by light and electron microscopy. The results will be correlated with ultrastructural changes in the infected red cell and the possible relationship between deep vascular schizogony and red cell membrane abnormality induced by the parasite examined. Daily examination of peripheral blood smears will demonstrate the period of maximum sequestration. When the peripheral parasitemia reaches approximately 1 percent the animals will be sacrificed. Crush preparations of the cerebrum, atrium ventricle, lung, liver, spleen, kidney, bone marrow, and skeletal muscle will be prepared and stained with phosphate buffered Giemsa at pH 7.2. In addition tissues from each organ will be fixed in Zenker's fluid for light microscopy and Dalton's dichromate buffered osmium tetroxide for electron microscopy. Analysis of crush preparations and tissue sections will be used to quantitatively determine organ distribution. Electron micrographs of serial sections of parasitized red cells will be analyzed and the radius of the curvature measured between knobs in the membrane of infected red cells and vessel endothelia to determine whether or not the knobs are the point of attachment to endothelium.